The use of microorganisms in various technologies and manufacturing processes has expanded greatly since the large scale production of antibiotics such as penicillin and since the culturing of aerobic microorganisms has been developed.
Culturing methods based on agitation and aeration were perfected and improved considerably during the past more than 40 years. A large number of publications appeared on this subject (e.g. "Biotechnology", vol. 2. Editor: Brauer, 1985).
In addition to special purpose devices such as devices for tissue cultures, reactors for the purification of effluent, etc. development concentrated mainly on the geometry of the fermentor, the determination of its dimensions and proportions, research and development directed to the shape of the agitators to develop a fermentor which can be universally applied to the production of aerobic culturing of microorganisms, such as in the production of antibiotics, enzymes and amino acids.
These technologies are generally characterized by high oxygen demand. The oxygen required for the metabolism of the microorganisms (dissolved oxygen for the deep-culture method) is mostly provided by agitation and aeration. Agitation and aeration simultaneously perform several important functions:
they assure homogeneity, the distribution of the nutrients in the entire volume of the ferment also in the outgoing metabolites;
provide oxygen supply by causing a considerable fluid gas boundary phase through the dispersion of the blown in air, thus assisting in the dissolution of the oxygen;
making use of the flushing effect of the air assures the removal of the gaseous products of the metabolism.
Most critical of the three functions if the supplying of oxygen. The greater the oxygen consumption of the microorganisms the more air and the more efficient dispersion i.e. agitation are required to assure an oxygen surplus. This however, increases manufacturing cost. Therefore, for a long time each way has been sought to eliminate the need for agitation. Solutions have been found, that at least partly meet this aim, but these have found only limited application. These solutions include the principle of the mammoth pump in which the agitator is surrounded by a large diameter pipe ending above the liquid level and air is blown into the pipe from below, beneath the agitator. A similar solution is the "air lift loop reactor" which employs blown air but in which no agitator is employed. While in these solutions less energy is required to move the fluid and assure relatively oxygen rich conditions within the pipe. The culture (ferment) pouring out on top of the pipe until it reenters the pipe must pass along a relatively long, dead, unaerated a space to which very few cultures can be exposed without damage.
Aeration by a fluid jet appears to be preferable. In such aeration a pump causes the ferment to circulate over an external circle by exhausting the fluid from the bottom of the fermentor and pressing it back to the fermentor (jet-reactor) dome as a jet under several atmospheres pressure. As the liquid jet passes through the space in top of the device it absorbs sufficient gas to endure the full oxygen surplus for the entire fermentor culture. Although the cost of power is very favorable in this use, the additional investment can be recaptured only in new fermentors and above a certain fermentor size.
The effort to reduce the specific power requirements led to a new fermentor called "TOURS" which consists of a horizontally arranged annular pipe in which the liquid moves both in a circle as well as up and down. The relatively large air space and the low hydrostatic pressure provides favorable conditions for the oxygen supply but also this device has its drawbacks; not only can its cost be amortised only in new fermentors, but it also has a considerably large footprint that requires large floor space. (A. Einsele Swiss Biotechn. 46/1986, p. 21-24).
None of the solutions outlined above is suitable to reduce at small extra cost the power demand of conventional fermentors.